In order to improve throughput of a computer system containing CPU (Central Processing Unit), memory, and the like, for example, improvements in a high integration and a high speed of a semiconductor memory device constituting the memory, particularly DRAM (Dynamic Random Access Memory) are proceeding. As an example of the improvements, such an instance can be offered that a memory should be composed of SDRAM (Synchronous DRAM) that operates in synchronism with a clock supplied from a clock generator to CPU (referred to as a “system clock” hereinafter). Also, various technologies regarding improvements in a structure of SDRAM and its utilizing method have been proposed, and the technology disclosed in Patent Literature 1 can be cited as an example. In this Patent Literature 1, the SDRAM that makes the mixed use of memory modules having different structures possible and the memory system including the same is disclosed.
Patent Literature 1: JP-A-2002-132580